This invention relates to improvements in an air intake structure of an internal combustion engine.
In internal combustion engines having a plurality of cylinders, in general, the more uniform the lengths of air induction pipes for respective cylinders are, the smaller the variation in volumetric efficiency of intake air among cylinders become, thereby achieving improvement in power output, reduction of vibration and the like while making uniform the waveform (height and phase) of noise generated by air suction of each cylinder so that the tone of noise becomes clear.
In this regard, Japanese Patent Provisional Publication No. 8-105359, discloses a technique in which a surge tank is disposed one-sided to upstream side air induction pipe placed in one end side in a cylinder row direction of an engine body, and the upstream ends of respective branch pipes of an intake manifold are located closer to the engine body as they come to the downstream side from the upstream side in intake air flow within the surge tank.